The present invention relates to a polishing method using chemical mechanical polishing (CMP), and more particularly to a polishing method suitable for use in the manufacture of semiconductor devices.
In association with the recent trend toward the high integration and miniaturization of semiconductor devices, various kinds of fine structure working technology are being researched and developed in the field of the manufacture of semiconductor devices. Among the various kinds of technology, the CMP technology can be used for many purposes, such as the flattening of the interlayer insulation film, the formation of plugs, the formation of buried metal wiring, and buried isolation of elements. The CMP technology, required for executing these, is now essential technology.
In the manufacture of semiconductor devices, there is a demand for a reliable process in which a silicon nitride film is polished using CMP, with a silicon oxide film used as a stopper. If such a process is available, it can be applied to the buried isolation of elements, the formation of a self-aligned contact, etc., thus enabling the fabrication of devices that are reliable and have high performance. However, in the case where conventional slurry is used, the ratio (selection ratio) of the polishing rate of a silicon nitride film to that of a silicon oxide film is smaller than 1. In this case, the process described above cannot be put to use.
As a method for realizing the above-described process, it is thought to prepare slurry by dispersing silica particles (polishing particles) in water and adding phosphoric acid to the water. The use of such slurry is proposed in Jpn. Pat. Appln. KOKAI Publication No. 6-124932. According to the method shown in this publication, it may be able to set the selection ratio to be larger than 1.
However, even when the method of KOKAI publication No. 6-124932 is used, it is hard to set the selection ratio to be sufficiently large. In particular, in the case of a fine pattern of 0.2 .mu.m or less, the substantial selection ratio is inevitably small.